1. Field of the Invention
The present invention generally relates to a damper mechanism. More specifically, the present invention relates to a damper mechanism for transmitting a torque while absorbing and damping torsional vibrations. The present invention also relates to a flywheel assembly, especially a flywheel assembly that is elastically coupled to a crankshaft in a rotational direction.
2. Background Information
A clutch disk assembly used in a vehicle has a clutch function for releasably engaging a flywheel, and a damper function for absorbing and damping torsional vibrations transmitted from the flywheel. In general, vibrations of vehicles include idling noises (rattling noises), driving noises (acceleration and deceleration rattling noises and muffled noises), and tip-in/tip-out (low-frequency vibrations). For suppressing such noises and vibrations, the clutch disk assembly is provided with a damper.
The idling noises are rattling noises, which are generated from a transmission when a clutch pedal is released after shifting a gear position to neutral, e.g., to stop at a traffic light. These noises are due to the fact that an engine torque is low and varies to a large extent in response to engine combustion when an engine speed is in or near an idling range. In or near the idling range, tooth collisions occur between an input gear and a counter gear of the transmission.
The tip-in/tip-out (low frequency vibrations) is a large longitudinal vibration of a vehicle body, which occurs when a driver rapidly depresses or releases an acceleration pedal. If a power transmission system has a low rigidity, a torque transmitted to tires is reversely transmitted from the tires to the power transmission system. This reaction causes an excessive torque to be transmitted to the tires so that large longitudinal vibrations transitionally occur to vibrate the vehicle body longitudinally to a large extent.
The idling noises are significantly affected by torsion characteristics of a clutch disk assembly at and around a zero torque, and can be effectively prevented by reducing a torsional rigidity at and around the zero torque. Conversely, for reducing the longitudinal vibrations of the tip-in/tip-out, torsion characteristics of the clutch disk assembly must be solid to a large extent.
For overcoming the above problems, a clutch disk assembly has been provided that uses two kinds of spring members for providing characteristics having two stages. In this structure, the torsional rigidity and a hysteresis torque are kept low in the first stage (low torsion angle region) of the torsion characteristics. This is effective in preventing noises during idling. Since the torsional rigidity and the hysteresis torque are kept high in the second stage (high torsion angle range) of the torsion characteristics, the longitudinal vibrations of tip-in/tip-out can be sufficiently damped.
Further, such a damper mechanism has been known that it can effectively absorb minute torsional vibrations without operating a large frictional resistance mechanism for the second stage when the minute torsional vibrations are applied, e.g., due to combustion variations of the engine in the second stage of the torsion characteristics.
The damper mechanism described above can be achieved by providing a frictional resistance generating mechanism having the following specific structures. The frictional resistance generating mechanism is arranged as a whole to operate in parallel with a spring member of a high rigidity in a rotational direction, and has a frictional resistance generating portion, and a rotating-direction engagement portion arranged to operate in series with respect to the frictional resistance generating portion in the rotational direction. The rotating-direction engagement portion has a minute rotating-direction space between two members.
In the prior art, the rotating-direction space can be configured to operate in response to minute torsional vibrations only in the second stage (large torsion angle region) of the torsion characteristics.
In some cases, however, vibration damping performance can be improved, when such a manner is employed that a large frictional resistance does not occur even when the torsion angle exceeds a predetermined angle in the first stage (small torsion angle region) of the torsion characteristics, and thus a large frictional resistance does not occur in response to the minute torsional vibrations.
Specifically, the damper mechanism described above is achieved by providing a frictional resistance generating mechanism having the following structure. This frictional resistance generating mechanism is arranged to operate in parallel with spring members, which have a high rigidity as a whole, in the rotating direction. Further, the frictional resistance generating mechanism has a frictional resistance generating portion and a rotating-direction engagement portion arranged to operate in series with respect to the frictional resistance generating portion in the rotating direction. The rotating-direction engagement portion is formed of a minute rotating-direction space between two members.
Accordingly, when minute torsional vibrations caused by combustion variations of an engine are generated, the minute rotating-direction space prevents the operation of the frictional resistance generating portion.
However, when torsional vibrations of a large torsion angle are applied, the frictional resistance generating portion operates, and the frictional resistance generating portion does not operate corresponding to the minute rotating-direction space only on the opposite sides, of the torsion angle range. Thus, a large frictional resistance suddenly occurs on the opposite sides of the torsion angle range when torsional vibrations of a large torsion angle are applied. This large frictional resistance increases the impact of collision between the members forming the rotating-direction space so that hitting or tapping noises occur.
In conventional damper mechanisms, a flywheel is fixed to a crankshaft of an engine for absorbing vibrations caused by combustion variations of the engine. Further, a clutch device is arranged on the transmission side of the flywheel in an axial direction. The clutch device includes a clutch disk assembly coupled to an input shaft of a transmission and a clutch cover assembly for biasing a frictional coupling portion of the clutch disk assembly with the flywheel. The clutch disk assembly has a damper mechanism for absorbing and damping torsional vibrations. The damper mechanism has elastic members such as coil springs, which are disposed for compression in the rotating direction.
A structure is also known such that the damper mechanism is arranged not in the clutch disk assembly but between the flywheel and the crankshaft. In this structure, the flywheel is located on an output side of a vibration system, in which the coil springs provide a boundary between the output and input sides, and an inertia on the output side is larger than that in a conventional structure. Consequently, a resonance rotation speed can be set below an idling rotation speed and a high damping performance can be achieved. The structure formed of the above combination of the flywheel and the damper mechanism provides the flywheel assembly or the flywheel damper.
When the flywheel assembly described above receives torque variations from an engine, the springs in the damper mechanism are compressed in the rotational direction to absorb and damp the torque variations. Further, the damper mechanism has a frictional resistance generating mechanism formed of a plurality of members, therefore sliding occurs in the frictional resistance generating mechanism to generate a predetermined hysteresis torque when springs are compressed. Consequently, torsional vibrations are rapidly damped.
The damper mechanism includes a pair of input plates opposed to each other, an output plate disposed between the input plates, and a coil spring circumferentially and elastically coupling the pair of input plates to the output plate. The pair of input plates is fixed together by a plurality of stop pins on the radially outer side so that the input plates rotate together. The stop pins are inserted into recesses formed at an outer periphery of a flange. The pair of input plates can rotate through a predetermined angle range with respect to the flange, and the relative rotation stops when the stop pins come into contact with the circumferential ends of the recesses. As described above, the stop pins couple the pair of input plates together as well as function as a stopper with respect to the flange.
The stop pin must have a certain diameter and must be disposed radially inside the outer periphery of the pair of input plates. Due to these conditions, it is impossible to increase a relative rotation angle between the input plate pair and the flange in the structure employing the stop pins. This means that the performance of coil springs cannot be fully utilized even if the coil springs have a high strength because the relative rotation angle cannot be increased sufficiently. For reducing tooth-hitting noises and muffled noises of a drive system during driving of a vehicle, it is necessary to minimize a torsional rigidity in an acceleration/deceleration torque range for setting a torsional resonance frequency of the drive system to a value lower than an actual rotation range. For achieving the low torsional rigidity and a further increased stopper torque, it is necessary to ensure a wide torsion angle.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved damper mechanism. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.